Vitamin D2 just as good as D3?

Challenging the view that vitamin D3 is more potent than D2,
researchers from Boston University have reported that both forms
are equally effective at maintaining 25-hydroxyvitamin D status.

Several studies have reported that vitamin D2 is between 30 and 50
per cent less effective as the D3 form in maintaining blood levels
in humans.
The new study, published in the Journal of Clinical
Endocrinology & Metabolism​, could challenge this view
however. The three-month study with 68 subjects found that
supplementation with both forms produced similar results.
Vitamin D refers to two biologically inactive precursors - D3, also
known as cholecalciferol, and D2, also known as ergocalciferol. The
former is produced in the skin on exposure to UVB radiation (290 to
320 nm). The latter is derived from plants and only enters the body
via the diet.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys
to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage'
form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically
active form that is tightly controlled by the body.
"Our results suggest that vitamin D2 is as effective as vitamin
D3 in sustaining both 25(OH)D and 1,25(OH)2D levels and improving
bone health,"​ wrote lead author Michael Holick.
"Our observations also suggest that 1,000 International Units
(IU) of vitamin D2 or vitamin D3 is required to sustain blood
levels of 25(OH)D above a mean of 20 ng/ml, but was insufficient in
raising the levels above a mean of 30 ng/ml." ​
Currently, the vitamin's RDA is 400 IU, but calls have been growing
louder to increase this level considerably. The new study appears
to support this view.
Holick and co-workers randomly assigned the subjects (average age
38.6) to one of four intervention groups for 11 weeks. The first
received placebo, the second received 1,000 IU (25 micrograms)
vitamin D2, the third received 1,000 IU (25 micrograms) vitamin D3,
and the fourth received 500 IU vitamin D2 plus 500 IU vitamin D3.
All supplements were manufactured by Tishcon Corp.
Sixty percent of the adults were vitamin D deficient at the start
of the study.
The Boston-based researchers report that adults in the placebo
group experienced no significant change in their total 25(OH)D
levels during the winter and early spring. Adults receiving
the vitamin D supplements all experienced similar 25(OH)D level
increases, however.
In addition, the 1,000 IU dose of vitamin D2 or D3 did not raise
25(OH)D levels in vitamin D deficient subjects above 30
ng/ml.
"One thousand IU of vitamin D2 daily was as effective as 1,000
IU of vitamin D3 in maintaining serum 25-hydroxyvitamin D levels
and did not negatively influence serum 25-hydroxyvitamin D
levels,"​ said Holick. "Therefore, vitamin D2 is equally as
effective as vitamin D3 in maintaining 25-hydroxyvitamin D
status."​
"More studies are needed to determine whether the media (i.e.,
ethanol vs oil vs lactose) that vitamin D2 and vitamin D3 are
dissolved in influence either their bioavailability or
catabolism,"​ concluded the researchers.
Commenting independently on the research, Daniel Fabricant, PhD,
vice president, scientific and regulatory affairs for US trade
association, the Natural Products Association (NPA) told
NutraIngredients.com: "It's an interesting area of study, as
with any such study it generally leads to more questions than it
answers. But it may bode well for vitamin D2, of course more
research will be needed." ​​"While this
study may continue to confound the understanding of optimal D
status, until the body of D2 clinical studies produce the results
the D3 studies have, D3 will most likely continue to be favored by
the research community." ​
Dr. Fabricant added that the analytical methodology of measuring
vitamin D also require attention since multitude challenges
currently exist.
"One issue with Liquid Chromatography/Mass Spectrometry (LC-MS)
is that it has a relative inability to discriminate between
25(OH)D3 and its inactive isomer 3-epi-25(OH)D3, additionally the
production of 25(OH)D2 as a result of vitamin D2 supplementation
may additionally hinder the assessment of total circulating
25(OH)D, apparently some common assay systems used for clinical
purposes have either a diminished capacity or do not detect
25(OH)D2 with the same efficiency as 25(OH)D3,"​ he said.
"It would be important to run some sort of comparative analysis
to determine whether this was also a factor in LC-MS analysis of
Vitamin D." ​
Previously, researchers from Creighton University in Omaha reported
in 2004 that while both forms of the vitamin do produce similar
rises in serum concentration of the native vitamin, indicating
equivalent absorption, only vitamin D3 sustained 25(OH)D levels
over a 14 day period. However, serum 25OHD fell rapidly in the
D2-supplemented subjects and was not different from baseline at 14
days.
Source: Journal of Clinical Endocrinology &
Metabolism​
Published online ahead of print, 18 December 2007.
doi:10.1210/jc.2007-2308
"Vitamin D2 is as effective as vitamin D3 in maintaining
circulating concentrations of 25-hydroxyvitamin
D" ​Authors: M.F. Holick, R.M. Biancuzzo, T.C. Chen, E.K.
Klein, A. Young, D. Bibuld, R. Reitz, W. Salameh, A. Ameri, and
A.D. Tannenbaum
Read NutraIngredients.com's report of the 2004 Creighton University
report here​.